Battery chargers typically charge one specific battery-operated device through a cable attachment or terminal connection and typically have charge times beyond one hour or so. That is, for example, a cell phone charger typically does not charge a digital camera and so forth. Such chargers also generally do not encompass a high rate charge connection or terminal allowing charge times under fifteen minutes. Recent developments in battery cells technology, including lithium-ion (Li-ion) rechargeable batteries, have made the idea of rapid battery charging in the range of minutes instead of hours a realistic expectation for consumers.
Li-ion rechargeable batteries typically are charged by a source that provides a constant current followed by a constant voltage (CC/CV) with a crossover from constant current to constant voltage at approximately 4.2V. That is, the charging operation switches from a constant current mode to a constant voltage mode when the battery's voltage reaches approximately 4.2V. The source that provides such a charging profile is controlled by an electronic feedback mechanism. Charging a rechargeable battery within a given period of time involves careful and accurate regulation of the charging device's charging mechanism. Facilitating accurate regulation of the charging current involves accurate measurement of the battery's voltage and/or current. Furthermore, because batteries have different capacities and require different levels of charging currents accurate information regarding battery capacities enables completion of the charging operation within the given period of time.
Conventional chargers rely on a mechanical or analog or digital technique to determine the type of battery being charged and thus an appropriate charge regime to apply. For example, some techniques are based on the use of an internal battery identification resistor, the value of which determines the charging parameters applied for that specific battery. Mechanical techniques have also been used, such as using the location of a connector polarity key or the location of a particular connector pin to distinguish between different battery models requiring different charging parameters. The Smart Battery Bus (SMBus) standards, for example, use a serial data communications interface to communicate the charging parameters to the charging device. The above approaches use additional connection points beyond the battery power terminals or some added mechanical feature not required for the basic battery function of delivering stored energy to a portable device. In the case of the SMBus standard, an electrical circuit and at least two additional connector pins are used to implement the smart interface between the charger and battery, adding to the cost, complexity and size of the battery.